Rake receiver with individual finger compensator(s)

ABSTRACT

Rake receivers in code division multiple access (CDMA) telecommunication comprise fingers ( 1,2,3 ) with each finger processing signal components for a particular transmission path to be able to better synchronize with a RF signal received via different paths, and a combiner ( 4 ) for combining the results originating from said fingers, and a compensator in the form of a controlled oscillator in a feedback loop. By locating a finger compensator ( 20 - 25 ) in a finger, said finger can handle complex situations, like Doppler shifts under high-speed conditions. Preferably, most or all fingers each comprise such a finger compensator, in which case said feedback loop can be avoided. Such a finger compensator can be hardware, software or a mixture of both when comprising a filter ( 21 ) plus an amplitude normalizer ( 22 ) between two arithmetical modules ( 20,25 ) for multiplying an input symbol signal with a conjugated previous input symbol signal and an output symbol signal with a previous output symbol signal.

The invention relates to a rake receiver comprising at least twofingers, a combiner coupled to said fingers and a compensator.

The invention also relates to a finger for use in a rake receivercomprising at least two fingers, a combiner coupled to said fingers anda compensator, and to a system comprising at least one portable unit andat least one network unit for radio communication, with at least oneunit comprising at least one rake receiver comprising at least twofingers, a combiner coupled to said fingers and a compensator, and to aportable unit comprising at least one rake receiver comprising at leasttwo fingers, a combiner coupled to said fingers and a compensator, andto a network unit comprising at least one rake receiver comprising atleast two fingers, a combiner coupled to said fingers and a compensator,and to a method for compensating signals in correspondence with at leastpart of a rake receiver and comprising at least two finger processingsteps, a combining step and a compensating step, and to a processorprogram product (like for example a software product or a computerprogram product) for implementing at least part of a rake receiver andcomprising at least two finger functions, a combining function and acompensating function to be run via a processor, and to a processorprogram product (like for example a software product or a computerprogram product) for implementing a finger and comprising a fingerfunction to be run via a processor and for use in combination with atleast part of a rake receiver at least partly implemented by at leasttwo finger functions, a combining function and a compensating functionto be run via said processor.

Rake receivers exploit multipath propagation (multipath propagation forexample exists when a transmitted signal, before receival, is reflectedvia buildings etc.) by letting fingers (or rake arms) separately processmultipath components of a transmitted signal and by then combining, forexample by using a combiner, their energies. Thereto, more particularly,said fingers (or rake arms) track and despread the multipath components.Such a rake receiver is for example used in code division multipleaccess (CDMA) telecommunication systems or wideband code divisionmultiple access (WCDMA) telecommunication systems, with said portableunit for example being a mobile phone and with said network unit forexample being a base station or a switch or a router or a bridge or aserver etc.

Such a rake receiver is known from EP 0 989 687 A2 which discloses arake receiver comprising three fingers, a combiner, of which inputs arecoupled to outputs of said fingers, and a compensator of which an inputis coupled to an output of said combiner and of which an output iscoupled via a controlled oscillator to an oscillator input of a mixerfor example for converting intermediate frequency signals into basebandsignals, which are supplied to said fingers. Each finger correspondswith a different transmission path and processes signal components forthis particular transmission path (finally, to be able to bettersynchronize with a RF signal received via different transmission pathsdue to reflections etc.) which processed signal components, togetherwith the processed signal components from the other fingers(corresponding with the other transmission paths), are all combined insaid combiner, and then further processed etc. Due to being locatedbetween an output of the combiner and inputs of said fingers via saidcontrolled oscillator and said mixer, this compensator makes afrequency-shift compensation for the entire rake receiver by controllingsaid controlled oscillator.

It is an object of the invention, inter alia, of providing a rakereceiver which can handle more complex situations.

The rake receiver according to the invention is characterized in that atleast one finger comprises a finger compensator.

By introducing said finger compensator in said finger, now, for examplein addition to having one compensation for the entire rake receiver, anindividual transmission path gets individual compensation via itsindividual finger comprising the individual finger compensator. Thisfinger compensator for example compensates output signals of thefinger's correlators. So, the finger compensator compensates symbolsignals (for example mathematically).

The invention is based upon a basic idea, inter alia, of creatingindividual compensations for individual transmission paths.

The invention solves the problem, inter alia, of providing a rakereceiver which can handle more complex situations, like for exampleDoppler frequency-shifts under high-speed conditions (like for exampleat 500 km/h), due to now not Oust) making a frequency-shift compensationper receiver, but for example in addition making a compensation perfinger (in other words making a compensation per transmission path).

A first embodiment of the rake receiver according to the invention asdefined in claim 2 is advantageous in that said finger compensator,comprising said filter like for example a FIR filter and said amplitudenormalizer, is of a low complexity and highly stable.

A second embodiment of the rake receiver according to the invention asdefined in claim 3 is advantageous in that this entire fingercompensator can be implemented in hardware, software or a mixture ofboth.

A third embodiment of the rake receiver according to the invention asdefined in claim 4 is advantageous in that said at least one finger,comprising the known pilot channel correlator and the known trafficchannel correlator, with an output of said finger compensator beingcoupled to first inputs of the third and fourth arithmetical module likefor example multipliers, of which second inputs are coupled to outputsof said correlators, allows a frequency-shift to be estimated by saidfinger compensator, after which said third and fourth arithmeticalmodules multiply a conjugated estimated frequency-shift with the outputsignals of both correlators for compensating the frequency-shift afterboth correlators.

A fourth embodiment of the rake receiver according to the invention asdefined in claim 5 is advantageous in that said at least one finger,further comprising the known averaging unit, of which an input iscoupled to an output of said third arithmetical module and of which anoutput is coupled to a first input of the fifth arithmetical module likefor example a multiplier, of which a second input is coupled to anoutput of said fourth arithmetical module, can be implemented inhardware, software or a mixture of both.

A fifth embodiment of the rake receiver according to the invention asdefined in claim 6 is advantageous in that most or preferably allfingers, each comprising said finger compensator, with all fingercompensators together forming said compensator, allow most or preferablyall transmission paths to be compensated individually.

A sixth embodiment of the rake receiver according to the invention asdefined in claim 7 is advantageous in that said rake receiver,comprising the mixer for converting intermediate frequency signals intobaseband signals, which mixer comprises an oscillator input coupled to astable oscillator, no longer needs to be supplied by a controlledoscillator in a feedback loop.

Embodiments, of the finger according to the invention, of the systemaccording to the invention, of the portable unit according to theinvention, of the network unit according to the invention, of the methodaccording to the invention, and of both processor program productsaccording to the invention correspond with the embodiments of the rakereceiver according to the invention.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments(s) described hereinafter.

FIG. 1 illustrates in block diagram form a rake receiver according tothe invention comprising fingers according to the invention,

FIG. 2 illustrates in block diagram form a finger according to theinvention comprising a finger compensator, and

FIG. 3 illustrates a flow chart showing a method according to theinvention and a processor program product according to the invention forimplementing a finger.

FIG. 1 illustrates in block diagram form a rake receiver according tothe invention comprising three fingers 1,2,3 according to the invention,of which the inputs are coupled to an output of an A/D converter 5 andof which the outputs are coupled to inputs of a combiner 4. An input ofA/D converter 5 is coupled to an output of a mixer 6, of which a firstinput receives for example Intermediate Frequency (IF) signals and ofwhich a second input is coupled to an output of a stable oscillator fordown converting said IF signals to baseband signals like for example anIn-phase (I) component and a Quadrature (Q) component which areoversampled and quantified into digital samples by said A/D converter(usually in parallel in which case A/D converter 5 comprises twosubconverters). These samples are supplied to all fingers 1,2,3, whichdespread and demodulate these samples into symbol signals.

FIG. 2 illustrates in block diagram form a finger 1,2,3 according to theinvention comprising a finger compensator 20-25 comprising anarithmetical module 20 like for example a multiplier 20 of which a firstinput forms the input of said finger compensator 20-25 and of which asecond input is coupled to an output of a delay introducer 23. An inputof delay introducer 23 is coupled to said first input of saidarithmetical module 20, of which an output is coupled to an input of afilter 21 like for example a FIR filter 21. An output of filter 21 iscoupled to an input of amplitude normalizer 22, of which an output iscoupled to a first input of an arithmetical module 25 like for example amultiplier 25. An output of multiplier 25 is coupled via a delayintroducer 24 to a second input of arithmetical module 25 and forms anoutput of said finger compensator 20-25.

Said finger 1,2,3 according to the invention illustrated in FIG. 2further comprises a known pilot channel correlator 10 (for despreading apilot channel and generating an instantaneous phase and amplitudeestimation) and a known traffic channel correlator 12 (for despreading adata channel) both controlled by a known PN tracker 11 (for estimatingand adjusting a phase offset between a received signal and locallygenerated spreading codes, with PN meaning Pseudo Noise Code and with PNtrackers as well as possible additional PN code generators, multipliersand integrators being known technologies). Inputs of said correlators10,12 and PN tracker 11 form the input of said finger 1,2,3. An outputof correlator 10 is coupled to said input of finger compensator 20-25and to a first input of an arithmetical module 13 like for example amultiplier 13, of which a second input is coupled to said output offinger compensator 20-25 and of which an output is coupled to an inputof a known averaging unit 15, like for example Weight Multiple SymbolAverage (WMSA) module. An output of correlator 12 is coupled to a firstinput of an arithmetical module 14 like for example a multiplier 14, ofwhich a second input is coupled to said output of finger compensator20-25 and of which an output is coupled to a first input of anarithmetical module 16, of which a second input is coupled to an outputof averaging unit 15. An output of arithmetical module 16 forms anoutput of said finger 1,2,3.

For example in code division multiple access (CDMA) telecommunicationsystems or wideband code division multiple access (WCDMA)telecommunication systems, RF signals are exchanged between portableunits like for example mobile phones and network unit like for examplebase stations or switches or routers or bridges or servers etc. Theseunits comprise a rake receiver for dealing with multipath receptions (inother words, said RF signals, for example due to reflections, arereceived via different paths, which are individually processed by saidfingers, after which the results are combined to be able to bettersynchronize with said RF signals). According to prior art, a rakereceiver comprises a feedback loop including a controlled oscillator (acompensator) for compensating fluctuations in frequencies (AutomaticFrequency Control or AFC). An input of this compensator is theretoeither coupled to a further output of each finger or to an output ofsaid combiner. However, such an AFC loop cannot handle Dopplerfrequency-shifts under high-speed conditions (like for example at 500km/h), due to different transmission paths generally requiring differentcompensations.

The invention is based upon the insight, inter alia, that AFC loopscannot handle Doppler frequency-shifts under high-speed conditions, dueto different transmission paths generally requiring differentcompensations, and is based upon the basic idea, inter alia, of creatingindividual compensations for individual transmission paths.

Thereto, as illustrated in FIG. 2, one or more of said fingers 1,2,3according to the invention are each provided with finger compensator20-25 which receives an input symbol signal from correlator 10, whichinput symbol signal via arithmetical module 20 and delay introducer 23is multiplied (conjugatedly) with a conjugated previous input symbolsignal, resulting in a combined signal which is filtered via filter 21,after which the amplitude is normalized via amplitude normalizer 22. Theresulting signal is an output symbol signal which via arithmeticalmodule 25 and delay introducer 24 is multiplied with a previous outputsymbol signal. Said combined output symbol signal is supplied toarithmetical modules 13 and 14 respectively to be multiplied(conjugatedly) with the conjugated output signals of correlators 10 and12, after which the output signal of arithmetical module 14 ismultiplied (conjugatedly) by arithmetical module 16 with a conjugatedoutput signal of arithmetical module 13 after this output signal ofarithmetical module 13 has been processed by averaging unit 15. Eithersaid arithmetical modules 13, 14, 16 and 20 also take care ofconjugating those signals which need to be conjugated or further modulesnot shown conjugate these signals, with said conjugating of signalsbeing a known technology.

As a result, for example by individualizing filter 21 and/or amplitudenormalizer 22, the finger compensator 20-25 allows each finger now beingable to deal with more complex situations, like for example Dopplerfrequency-shifts under high-speed conditions. Further, the entire fingerincluding the finger compensator can be made in software, which is veryflexible, or in hardware, which is very fast, or in a mixture of both.So, each block shown in FIGS. 1 and 2, can be 100% hardware, 100%software or a mixture of both. Each block shown in FIGS. 1 and 2 can beintegrated with each other block shown in FIGS. 1 and 2.

In the flow chart illustrated in FIG. 3 and showing a method accordingto the invention and a processor program product according to theinvention for implementing a finger, the following blocks have thefollowing meaning:

Block 30: PN tracking the phase between a received signal and local PNcodes;

Block 31: Despreading samples with a local PN code for estimatingchannel parameters, the result is an input symbol signal;

Block 32: Despreading samples with a local PN code for generating userdata;

Block 33: Multiply (conjugatedly) said input symbol signal with aconjugated previous input symbol signal;

Block 34: Filter this multiplied input symbol signal;

Block 35: Normalize an amplitude of this filtered multiplied inputsymbol signal, the result is an output symbol signal;

Block 36: Multiply said output symbol signal with a previous outputsymbol signal;

Block 37: Multiply (conjugatedly) said input symbol signal with aconjugated multiplied output symbol signal, the result is a firstcombination signal;

Block 38: Multiply (conjugatedly) said user data with said conjugatedmultiplied output symbol signal, the result is a second combinationsignal;

Block 39: Calculate an average of said first combination signal;

Block 40: Multiply (conjugatedly) a conjugated average of said firstcombination signal with said second combination signal.

Each one of said blocks 30-40 corresponds with a (sub)step of a methodand/or with a (sub)function of a processor program product, with further(sub)steps and/or (sub)functions not to be excluded, as stated below.The method according to the invention and the processor program productaccording to the invention for implementing a finger function asfollows.

The received signal, when ignoring Multiple Access Interference (MAI)and Intersymbol Interference (ISI), at the inputs of blocks 30, 31 and32 can be written asr(t)=exp(j·Δω·t)·{Σh(n)·C _(pilot) [t−nT _(s) ]+σa(k)··h(k)·C _(traffic)[t−nT _(s) ]+m(t)},with r(t) being the received complex signal, n being a symbol number,h(n) being a wireless propagation parameter (assumed to be static in onesymbol time), C_(pilot)(t) being a spreading signal of a pilot channelincluding a PN code and a chip waveform, C_(traffic)(t) being aspreading signal of a traffic channel, a(n) being a symbol signal, Δωbeing a carrier frequency offset, m(t) being noise, and T_(s) being asymbol period. Ignoring the interference from traffic signals and noisem(t), at the output of block 31, the pilot correlator's output signalcan be written as

$\begin{matrix}{{{P(n)}\left( {\Delta\;\omega} \right)} = {{{INT}\left\lbrack {{nT}_{s}->{\left( {n + 1} \right)T_{s}}} \right\rbrack}\mspace{14mu}{of}\mspace{14mu}{{r(t)} \cdot {C_{pilot}^{*}\left\lbrack {t - {nT}_{s}} \right\rbrack}}{dt}}} \\{= {{{INT}\left\lbrack {{nT}_{s}->{\left( {n + 1} \right)T_{s}}} \right\rbrack}\mspace{14mu}{of}\mspace{14mu}{{\exp\left( {{j \cdot \Delta}\;{\omega\; \cdot t}} \right)} \cdot {h(n)} \cdot}}} \\{{{C_{pilot}\left\lbrack {t - {nT}_{s}} \right\rbrack} \cdot {C_{pilot}^{*}\left\lbrack {t - {nT}_{s}} \right\rbrack}}{dt}} \\{{= {{h(n)}{{\exp\left\lbrack {{j \cdot \Delta}\;{\omega \cdot \left( {{n \cdot T_{s}} + {T_{s}/2}} \right)}} \right\rbrack} \cdot \left\lbrack {{2 \cdot {{\sin\left( {\Delta\;{\omega \cdot {T_{s}/2}}} \right)}/\Delta}}\;\omega} \right\rbrack}}},}\end{matrix}$with ‘INT[nT_(s)→(n+1)T_(s)] of’ being the integral from nT_(s) to(n+1)T_(s) of etc. When there is no carrier frequency offset, Δω=0, aperfect wireless propagation parameter can be written asP(n)(0)=h(n)·T _(s).Then the influence of Δω to the correlator can be written asF(Δω)=P(n)(Δω)/P(n)(0)=exp[j·Δω·(n·T _(s) +T _(s)/2)]·[2·sin(Δω·T_(s)/2)/(T _(s)·Δω)].Obviously, there are two influences of the carrier frequency offset(Δω), namely an amplitude fading [2·sin(Δω·T_(s)/2)/(T_(s)·Δω))] and aphase shift comprising a variable (n-dependent) phase shift Δω·n·T_(s)and a fixed phase shift Δω·T_(s)/2. The amplitude fading is very smalland can be tolerated. At the output of block 33, when ignoring amplitudefading and assuming that the wireless propagation parameter shows littlevariation in one symbol period, in other words h(n)=h(n−1), the signalcan be written asP(n)(Δω)·P*(n−1)(Δω)=|h(n)|²·exp[j·Δω·T _(s)].After FIR filtering and amplitude normalizing, at the output of block35, the phase shift estimation can be written asS(n)=exp[j·Δω·T _(s)].At the output of block 36, a compensation signal can be written asΦ(n)=Φ(n−1)·S(n)·exp[j·{n·Δω·T _(s)+Φ(0)}],with Φ(0) being a fixed initial phase. Then, the pilot symbol signalafter compensation, when ignoring amplitude fading, can be written asP′(n)=P(n)·Φ*(n)=h(n)·exp[j·{Δω·T _(s)/2−Φ(0)}].Similarly, the traffic symbol signal after compensation can be writtenasQ′(n)=Q(n)·Φ*(n)=a(n)·h(n)·exp[j·{Δω·T _(s)/2−Φ(0)}].Both equations just show a fixed phase {Δω·T_(s)/2−Φ(0)} which has noeffect and is eliminated by block 39, resulting in the influence of thecarrier frequency offset being reduced.

Each one of the equations and/or formulaes states above and each part ofthe equations and/or formulaes states above could be considered to be afurther (sub)step of a method according to the invention and/or to be afurther (sub)function of a processor program product according to theinvention. Said finger compensator, said finger according to theinvention as well as at least most parts of said rake receiver accordingto the invention can now be implemented in the form of software via forexample a digital signal processor, which is very flexible and furtheradvantageous due to being written only once for millions of units. Butalso when implemented in the form of hardware, the invention still isvery advantageous due to being very stable and allowing compensators infeedback loops to be avoided.

1. Rake receiver for receiving information symbols, comprising at leasttwo fingers and a combiner coupled to said fingers, wherein each of theat least two fingers comprises a finger compensator that compensates forfrequency shift at the symbol level, wherein said finger compensatorcomprises: a filter and an amplitude normalizes coupled seriallyconfigured to receive an input symbol signal and configured to generatean output symbol signal; and a first arithmetical module configured tomultiply said input symbol signal with a conjugated previous inputsymbol signal and a second arithmetical module configured to multiplysaid output symbol signal with a previous output symbol signal, whereinat least one finger comprises: a pilot channel correlator and a trafficchannel correlator, with an output of said finger compensator beingcoupled to first inputs of a third and fourth arithmetical module, ofwhich second inputs are coupled to outputs of said correlators; and anaveraging unit, of which an input is coupled to an output of said thirdarithmetical module and of which an output is coupled to a first inputof a fifth arithmetical module, of which a second input is coupled to anoutput of said fourth arithmetical module.
 2. Rake Receiver according toclaim 1, wherein all fingers each comprise a finger compensator, withall finger compensators together forming said compensator.
 3. Rakereceiver according to claim 2, wherein said rake receiver comprises amixer configured to convert intermediate frequency signals into basebandsignals, which mixer comprises an oscillator input coupled to a stableoscillator.
 4. The Rake receiver according to claim 1, wherein said atleast one finger further comprises a plurality of delay paths.
 5. Asystem comprising at least one portable unit and at least one networkunit capable of radio communication, with at least one unit comprisingat least one rake receiver configured to receive information symbols,the at least one rake receiver comprising at least two fingers, and acombiner coupled to said fingers, wherein the at least two fingers eachcomprises a first arithmetical module configured to multiply an inputsymbol signal with a conjugated previous input symbol signal and afinger compensator that compensates for frequency shift at the symbollevel, wherein the finger compensator is coupled to inputs of at leasttwo arithmetical modules in a first set of arithmetical modules and atleast one finger comprises an averaging unit coupled between at leasttwo arithmetical modules in a second set of arithmetical modules, andwherein at least one arithmetical module is common to the first andsecond sets of arithmetical modules.
 6. The system according to claim 5,wherein said finger compensator comprises a filter and an amplitudenormalizer coupled serially configured to receive the input symbolsignal and configured to generate an output symbol signal.
 7. The systemaccording to claim 6, wherein said finger compensator further comprisesa second arithmetical module configured to multiply said output symbolsignal with a previous output symbol signal.
 8. The system according toclaim 7, wherein at least one finger comprises a pilot channelcorrelator and a traffic channel correlator, with an output of saidfinger compensator being coupled to first inputs of a third and fourtharithmetical module, of which second inputs are coupled to outputs ofsaid correlators.
 9. The system according to claim 8, wherein said atleast one finger comprises said averaging unit, of which an input iscoupled to an output of said third arithmetical module and of which anoutput is coupled to a first input of a fifth arithmetical module, ofwhich a second input is coupled to an output of said fourth arithmeticalmodule.
 10. The system according to claim 5, wherein all fingers eachcomprise a finger compensator, with all finger compensators togetherforming said compensator.
 11. The system according to claim 10, whereinsaid rake receiver comprises a mixer configured to convert intermediatefrequency signals into baseband signals, which mixer comprises anoscillator input coupled to a stable oscillator.
 12. The systemaccording to claim 5, wherein said finger compensator further comprisesa plurality of delay paths.
 13. Portable unit comprising at least onerake receiver configured to receive information symbols, the at leastone rake receiver comprising at least two fingers and a combiner coupledto said fingers, wherein the at least two fingers each comprises a pilotchannel correlator, a traffic channel correlator, and a fingercompensator that compensates for frequency shift at the symbol level,wherein the finger compensator is coupled to inputs of at least twoarithmetical modules in a first set of arithmetical modules and at leastone finger comprises an averaging unit coupled between at least twoarithmetical modules in a second set of arithmetical modules, andwherein at least one arithmetical module is common to the first andsecond sets of arithmetical modules.
 14. The unit according to claim 13,wherein said finger compensator comprises a filter and an amplitudenormalizer coupled serially configured to receive an input symbol signaland configured to generate an output symbol signal.
 15. The unitaccording to claim 14, wherein said finger compensator further comprisesa first arithmetical module configured to multiply said input symbolsignal with a conjugated previous input symbol signal and a secondarithmetical module configured to multiply said output symbol signalwith a previous output symbol signal.
 16. The unit according to claim15, wherein with an output of said finger compensator being coupled tofirst inputs of a third and fourth arithmetical module, of which secondinputs are coupled to outputs of said correlators.
 17. The unitaccording to claim 16, wherein said at least one finger comprises saidaveraging unit, of which an input is coupled to an output of said thirdarithmetical module and of which an output is coupled to a first inputof a fifth arithmetical module, of which a second input is coupled to anoutput of said fourth arithmetical module.
 18. The unit according toclaim 13, wherein all fingers each comprise a finger compensator, withall finger compensators together forming said compensator.
 19. The unitaccording to claim 18, wherein said rake receiver comprises a mixerconfigured to convert intermediate frequency signals into basebandsignals, which mixer comprises an oscillator input coupled to a stableoscillator.
 20. Network unit comprising at least one rake receiverconfigured to receive information symbols, the at least one rakereceiver comprising at least two fingers and a combiner coupled to saidfingers, wherein the at least two fingers each comprises a firstarithmetical module configured to multiply an input symbol signal with aconjugated previous input symbol signal and a finger compensator thatcompensates for frequency shift at the symbol level, wherein the fingercompensator is coupled to inputs of at least two arithmetical modules ina first set of arithmetical modules and at least one finger comprises anaveraging unit coupled between at least two arithmetical modules in asecond set of arithmetical modules, and wherein at least onearithmetical module is common to the first and second sets ofarithmetical modules.